Mosquito season in Onondaga County, NY: when it starts and ends

Mosquito months in Onondaga County

In a normal year mosquito season in Onondaga County, NY starts around April 27 and ends around October 17, about 25 weeks.

1. Jan
2. Feb
3. Mar
4. Apr
5. May
6. Jun
7. Jul
8. Aug
9. Sep
10. Oct
11. Nov
12. Dec

What to do in Onondaga County, and when

• Start tipping out standing water weekly by April 13.
• Book any yard treatment for late April, ahead of the July peak.
• Repellent can go away after October 17.
• 10 West Nile cases since 2016: you should wear EPA-registered repellent at dusk July to July, and check NY spray notices.

Onondaga County against the rest of NY

Onondaga County has the 24th longest season of 62 NY counties, at 173 days against 218 in New York County and 125 in Franklin County. Its mean temperature is 47.7°F.

• Genesee County: April 27 to October 17 (174 days, 1 WNV)
• Livingston County: April 27 to October 17 (173 days, 2 WNV)
• Cayuga County: April 28 to October 16 (171 days, 0 WNV)
• Seneca County: April 28 to October 16 (171 days, 0 WNV)

West Nile in Onondaga County

From 1999 to 2025, CDC ArboNET counted 29 human West Nile cases in Onondaga County (20 neuroinvasive) across 10 years. The worst was 2012 with 9; the latest was 2025.

See how the dates are worked out, and reading the West Nile counts.